Tomography is an imaging method in which x-ray projections are recorded from different projection angles. In this method a recording unit, comprising an x-ray source and an x-ray detector, rotates around an axis of rotation and also around an object to be examined. The x-ray detector is generally constructed from a plurality of detector modules which are disposed linearly or in a two-dimensional lattice. Each detector module of the x-ray detector comprises a plurality of detector elements, wherein each detector element can detect x-ray radiation. The detector elements correspond to individual picture elements of an x-ray projection recorded with the x-ray detector. The x-ray radiation detected by a detector element corresponds to an intensity value. The intensity values form the starting point for reconstruction of a tomographic image.
The x-ray radiation emanating from the x-ray source is scattered during the recording of an x-ray projection by the irradiated object, so that as well as the primary rays of the x-ray source, scattered rays also strike the x-ray detector. The scattered rays cause noise in the x-ray projection or in the reconstructed image and therefore reduce the detectability of differences in contrast in the x-ray image. To reduce scattered radiation influences an x-ray detector can have a collimator which causes only x-ray radiation of a specific spatial direction to fall on the detector elements. Such a collimator typically has a number of collimator bridges with a number of collimator modules. The individual collimator modules have absorber walls for absorption of scattered radiation and are aligned to the focus of the x-ray source.
Collimators are known for example from the publication DE 10 2010 062 192 B3. The publication describes self-supporting collimator bridges which are manufactured by gluing together collimator modules. These collimator bridges have a high level of rigidity and thus allow reliable collimation. However the manufacturing of such collimator bridges is only described on the basis of already produced collimator modules. It is further disclosed that an especially high inherent rigidity is able to be achieved with collimator modules manufactured in one piece.
In modern computed tomography large x-ray detectors curved along two spatial directions are used. In other words the detector modules have submodules which are disposed tilted in relation to one another such that a detector module curved along the axis of rotation is embodied. Previously self-supporting collimators have not been used for such x-ray detectors but the collimator modules are directly attached to the submodules. This is because the collimators for such x-ray detectors have increased rigidity and production accuracy requirements. In order to guarantee these requirements it is also necessary to optimize the manufacturing process for collimator modules.